Reamer segment and method of producing same



J n- 1951 w. H. EVANS 7,

REAMER SEGMENT AND METHOD OF PRODUCING SAME Filed July 8, 1946 Patented Jan. 9, 1951 REAMER SEGMENT AND METHOD OF PRODUCING SAME William H. Evans, Chicago, Ill.

Application July 8, 1946, Serial No. 681,845 2 Claims. (01. 7772) My invention relates to a reamer segment and method of producing the same and is a continuation-in-part of my prior co-pending application, Serial No. 497,035, filed August 2, 1943, patented June 3, 1947, #2,421,490.

My co-pending application, above reierredto, describes and claims an improved reamer particularly designed for reaming a blind hole, but many of the features of which are useful in the production of other types of reamers.

Among the featuresarea support for the seg ments such that they are firmly held in position on the mandrel and will not rock. With constructions'of this type, it is possible to produce a very sharp. blade because thereis no rounding of the cutting edge 'such as occurs when chattering or rocking takes place.

The principal object of my invention is the provision of an improved reamer segment particularly adapted for use with the reamer construction defined in the parent application.

Another object is the provision of an improved method of forming reamerhbladesn Still another object is the provision of an improved method of producing and sharpening reamer blades of the type identified.

In accordance with the general features of my invention, the reamer blade is formed from a solid piece of tool steel and machined by suitable means such as millin machines and the I like to form spirally disposed teeth on the exterior and means for supporting the segment on the mandrel on the internal face thereof. When the segment has been formed to substantially its desired final shape, it is hardened by heat treatment, case hardened to form a hard adhering case and then chromium plated to form a surface, the purpose and function of which will be explained. The peripheral surface of the metal removing teeth is then ground to finished form, leaving a sharp cutting edge but with the outermost surface softin a manner and for a purpose which will be described.

The invention is describedin connection with the accompanying drawing wherein Fig.1 is an elevational view of a reamer;

- Fig. 2 is a sectional view taken on the line 2-2 of Fig. l; V Y Fig. 3 is an enlarged fragmentary sectional View through one of the reamer teeth after all of the steps have been carried out thereon except the final grinding and sharpening step;

Fig. 4 is a view similar to Fig. 3 showing the completed reamer tooth;

Fig. 5 shows'the condition of the toolwhen partly worn and indicates original top surface; and

Fig. 6 shows the condition of the cutting edge at maximum wear and indicates the manner of sharpening to restore initial cutting eificiency.

Referrin now to the drawing, I show in Fig. 1 areamer corresponding to that shown in the prior co-pending application in which cutting segments I 9 are supported on a mandrel II by suitable means. As shown in Fig. 2, this may comprise a hook-like engagement between the mandrel and segments such that when the reamer is rotated in the direction shown by the arrow, the segments will be drawn tightly against the mandrel and any tendency toward lifting, rocking or chattering will be eliminated. Preferably, in a reamer of this type, there are three blades and the cutting teeth are oppositely spiralled so that one set of teeth will cut across the tool marks of another to eliminate the possibility of discontinuity of the desired mirror finish.

The cutting segments "are provided with flutes l2 and lands l3, the latter, for convenience, being sometimes hereinafter called teeth and having a construction andfunction as will be explained. The flutes and lands may be formed in various ways but suitably they are cut on an eighteen inch lead, that is to say, equivalent to one threadin about eighteen lineal inches. This structure of detail may be varied somewhat, particularly in different sizes but I have found that a pitch or lead of about eighteen inches will produce good results and will be suitable for most purposes. While the pitch or lead may vary, there is an advantage in standardizing this structural feature, particularly from the standpoint of decreasing cost of production and facilitating sharpening. It is not essential that the surfaces be on a regular curve but various forms may be utilized. A suitablewidth across the lands is about 1% of an inch in reamers of medium size running generally between about of an inch and 1% of an inch. Above and below these sizes, it may be necessary to modify this dimension. From the leading or cutting edge of the land to the trailing edge thereof, there is a drop of about .0025 of an inch, although this dimension may also be modified.

Because of the structural features described in my prior application, and shown generally in Fig. 2, the segments engage the mandrel tightly and there is no possibility of a chatteringaction-or digging in of the cutting surfaces.

the position of the A sharp reamer will, therefore, produce a mirror finish. The features of my invention may be utilized with any suitable construction which will permit a firm holding of the cuttin blades.

Preferably a high speed tool steel such as high molybdenum tool steel, known in the trade as Latrob Double Six tool steel, is employed, for producing the cutting segments. While in the unhardened condition the steel is shaped. substantially to finished form but without finishing the top of the lands to produce the cutting teeth. The top of the teeth then has approximately the shape indicated in Fig. 3. The tool steel may then be hardened to substantially its maximum hardness; or, as an alternative or additional procedure to produce maximum hardening, the segments are case hardened by any suitable means which will produce a very thin case hardened surface such as indicated by the numeral 14. While any suitable case hardening method may be employed in producing this case hardened surface i i, 1 have obtained good results by using a process in which the surface of the steel is hardened by nitriding. The case hardened segment is then treated to form a chromium plate Hi. Thereafter the segment is sharpened by grinding the top of the teeth along a diagonal line A to produce a drop from'the leading edge I? to the trailing edge i8 of the order desired. As noted hereina-bove, a drop of about .0925 of an inch across 6 inch of tooth surface produces a very satisfactory cutting segment in which the cutting occurs at the leading edge I'I. It will be noted from the manner of producing the segment that the top surface of the final tooth, as shown in Fig. 4, is soft but the leading surface, forming with the top surface the cutting edge 17, is very hard. The top surface, therefore, can quite readily Wear away so that as wear occurs at the leading edge the blade will remain sharp until it wears substantially to a horizontal line B in which there is no drop from leading to trailing edge. This line is shown dotted in Fig. 5 but comprises the upper surface of the structure as shown in Fig. 6 in which the tool has been used until the maximum amount of useful life without resharpening has been obtained from it. In Fig. 5, the original position of the upper edge is indicated by the dotted line A. Thus as the tool wears during use from substantially the position shown in the line A to substantially the position of the line B, it remains sharp and performs useful service. Those skilled in the art will understand that this showing is on an enlarged scale and only approximately indicates the exact condition but that this condition can readily be determined by inspection of the blade itself. When the cutting segment has been worn to the maximum practical amount, it is resharpened by again grinding along the line C (Fig. 6) to produce a structure substantially identical with that in Fig. 4, but wherein the overall height of the lands is slightly decreased. In an expansion reamer this is, readily compensated for by merely expanding the segments a greater distance along the mandrel.

I have found that notwithstanding the fact that a very hard cutting edge is produced, that edge will not flake off but will remain sharp until the top surface is substantially flat as indicated by the surface B in Fig.6. This may be contrasted with that of usual reamer segments with which I am acquainted wherein the cutting edge, instead of remainingsharp, becomes rounded. The ability of the top surface to wear readily and the extreme hardness of the front surface produces a sharp cutting edge such that it is self-sharpening and will have a tendency to wear sharp even though for some reason or other it might not be finished fully sharp when produced.

The thin coating of a noble metal such as chromium (iridium or like materials may also be used) prevents any tendency for metal particles to adhere to, the cutting edges. I have found that otherwise there is a tendency, particularly when cutting certain types of metals, for metal particles'to adhere and cause a streaked finish .on the reamed surface. For example, if a protecting coating is not employed as described, and the reamer used to ream aluminum and bronze, very small particles of aluminum will adhere to the cutting edges and out very fine score lines in the bronze.

Those skilled in the art will understand that the steps of producing the segment comprise first producing the reamer substantially to its final form and after such production, then in the order of steps given to harden the metal, case harden the metal to form a very thin but :hard case, then chromium plate the teeth and finally sharpen them in the manner shown and described.

What I claim as new and desire to protect by Letters Patent of "the United States is:

1. A process of manufacturin a removable reamer blade having a cutting tooth comprising the steps of finish machining the front and back surfaces of the cutting tooth but not the top surface thereof, uniformly hardening the blade and cutting tooth, case hardening the cutting tooth, chromium plating the cutting tooth, and grinding the top surface of the chromium plated cutting tooth on a slant behind the cutting edge thereof for sharpening the cutting tooth by producing a clearance behind the cutting edge and for removing the chromium from the top surface behind the cutting edge but leaving unground the chromium on the front and back surfaces of the cutting tooth.

2. A removable reamer blade comprising a segment structure having a cutting tooth formed thereon, the segment structure and cutting tooth being uniformly hardened, the front and rear surfaces of the cutting tooth being finished machined, case hardened and coated with chromium plate, and the top surface of the cutting tooth being finished ground on a slant behind the cutting edge of the cutting tooth to provide a clearance behind the cutting edge and being uncoated with chromium plate and softer than the front and rear surfaces of the cutting tooth.

WILLIAM H. EVANS.

REFERENCES CITED The following references are of record in the file of this patent:

UNITED STATES PATENTS OTHER REFERENCES Mechanical Applications of Chromium Plating, Mechanical Engineering, December 1928, pages 927 to 930, vol. 50, No. 12.

Hard, Corrosion-Resistant, Slippery, Metals in Industry, from Scientific American, September 1943, pages 112 to 114.

Are Nitrided Cutting Tools Successful- Machinery, vol. 39, No. 12, August 1933, pages 753 to 758.

Chromium Plating Increases the Life of Tools and Dies in Automotive Plants, Machinery, May 1934, pages 536 to 537. 

